1. Field of the Invention
This invention relates to protecting human subjects exposed to high levels of acceleration. More particularly, it relates to applying buoyancy induced forces to the human body to expand the limits of useful consciousness, and reduce the risk of injury.
2. Description of the Related Art
Modern high performance fighter aircraft are capable of flight maneuvers which subject the crew members to very high forces of acceleration. Severe stresses are placed on the crew members by such aircraft maneuvers. Indeed, many modern aircraft are capable of aerial maneuvers which are beyond the tolerance of the human crew members. Consequently, fighter aircraft and their crew members are occasionally lost as a result of pilot blackout.
Aircraft equipment malfunction or adverse environmental conditions may occasionally make proper control of the aircraft so difficult as to render it improbable that the aircraft can be safely landed. Enemy fire in combat situations may seriously disable an aircraft or crew member making it also improbable that the aircraft can be brought to a safe landing. In such situations, ejection of the crew members from the aircraft may be desirable. However, in some such situations, the high forces of acceleration generated by catapult ejection systems may be added to the forces generated by the motion of the aircraft and the total forces may thus exceed the tolerance of the crew members. Consequently, pilots and their crew members are occasionally killed or severely disabled as a result of ejection from an aircraft.
Several approaches have been proposed for solving the problem of High "G" Forces. For example, co-applicant S. G. Wurst is the applicant of a copending patent application Ser. No. 175,660 entitled, "High 'G' Protection System"now U.S. Pat. No. 4,834,322, issued May 30, 1989. That patent application (assigned to the present assignee, Rockwell International Corporation) discloses a seat restraint system for supporting the occupant in a leaned forward or crouched position. This results in a reduced hydrostatic column between the aorta and retina of the eye and thus the acceleration to which the occupant is exposed can be raised. Although such a restraint system results in enhanced vehicle occupant capability in the face of high acceleration forces, the occupant is still subjected to physical strain. The strain results from the skeleton having to support the acceleration induced increase in weight of the body masses.
Co-applicant W. J. Adams is a co-applicant of a co-pending patent application, Ser. No. 249,794, entitled "Head Support/Spine Offloading Ejection Seat Insert" (also assigned to the present assignee). That patent application discloses a device insertable within the existing seat of a vehicle for maintaining a crew member of the vehicle in a forward posture during high g acceleration. The seat insert reduces the risk of spinal injury by offloading the crew member's spine and supporting the spine in its natural curvature, thereby preventing harmful bending of the spine and non-uniform load distribution across individual vertebrae interfaces.
Beginning in the 1940's, numerous studies were conducted at various centrifuges to determine the effect of water immersion on human g tolerance. The most notable of these efforts was conducted in 1958 at the Naval Air Development Center Centrifuge, in Johnsville, Pa. As reported by R. F. Gray and Lt. Cdr. M. G. Webb in "High G Protection", Aerospace Medicine, May 1961, subjects tolerated +16 g.sub.z and +31 g.sub.x when submersed in a water-filled capsule. The effect of submersion in a water capsule has also been studied at the Mayo Clinic, including tests conducted as early as 1943 by E. H. Wood.
The first practical water-filled g suit was developed during World War II. The suit, which resembled a pair of hip waders, was found to increase g tolerance by 11/2 g's. It was also found that inflating the suit with air, which was lighter and less cumbersome, also provided a 2.2 g increase in g tolerance (Lambert, E. H., Wood, E. H., Baldes, E. J., and Code, C. F., Report Number 248, Office of Scientific Research and Development, 19 Jan. 1944. Lambert, E. H., Wood, E. H., Baldes, E. J., and Code, E. F., Report Number 308, Office of Scientific Research and Development, 27 May 1944.). After many more modifications, the standard pneumatic g suit eventually evolved from these studies. The standard g suit provides a 2 to 2.5 g improvement in g tolerance.
U.S. Pat. No. 2,228,115, issued to M. R. Holste, discloses a water-filled suit which covers the entire body including the feet and hands from the base of the neck down to the bottom of the feet. The garment is formed of flexible inner and outer walls to form attenuated or thin chambers that contain water that is free to circulate therein. The inner shell is collapsable and may be of elastic material. The outer shell should be quite inelastic, although very flexible. The suit is supported by a frame which contains a metal yoke around the neck to which the suit is attached.
The Holste device is deficient in that during its use there would be distension of the carotid artery due to the heartbeat pulse triggering the stretch receptors to reduce heart output pressure. Furthermore, no means are provided to assure that the hydrostatic pressure column within the suit is kept at an appropriate level during use so as to prevent the application of too much pressure or too little pressure to the wearer's body. Furthermore, during use, the excessive pressure exerted on the chest by the suit will hinder pilot breathing. No means are provided to assist pilot breathing.
U.S. Pat. No. 2,335,474, issued to H. W. Beall, discloses a suit consisting of a snuggly fitting inner body garment portion and a spaced outer garment portion. The spaced outer portion forms a sack of fluid-tight compartments in the form of long, narrow sack members in free communication with each other. The suit contains a neck band which is pressurized with air when required for crew protection. This suit design is deficient in that the fluid-tight compartments or tubes become circular when exposed to acceleration, reducing the surface area in contact with the wearer. As a result, longitudinal areas are formed, running the length of the wearer's body, which are not covered by the tubes. These areas provide paths for blood to flow directly down to the feet, an undesirable result. A reservoir is provided for filling and draining the suit. In operation water is pumped from the reservoir into the suit before g onset and then the suit is drained after the g episode. Such a draining and filling concept could not be made to operate fast enough for use with today's highly manueverable aircraft.
U.S. Pat. No. 4,546,491, issued to R. B. Beaussant, discloses a garment having pockets and a regulator for controlling the air pressure within the pockets. The device includes a regulator which control air pressurization of the garment. The trouser pockets are partially filled with water. Utilizing pockets with upper compartments for pressurized air and lower compartments for water is potentially injurious inasmuch as too much pressure is exerted o the portion of the legs covered with water. (The pressure exerted is the sum of the air pressure and water pressure.) Furthermore, the Beaussant device, like the Holste and Beall devices is deficient with respect to its ability to provide a desired counterpressure to the neck.